Many types of manufactured parts must be coated with various substances in order to achieve the necessary or preferred characteristics before they may be used. These parts, however, often include surface portions (e.g., internal surface portions) that should not be coated. Most parts often include one or more openings which during the coating process allow coating materials to come in contact with internal surface portions of the part. Depending on the specific application for the part, contact between the coating and the internal surface portions of the part can be undesirable and/or can severely damage the part. An estimated 9.8 million dollars are spent each year on rework to ensure quality.
Often the openings are threaded in order to engage with a threaded fastener or other part. The threads must engage the fastener or other part perfectly and the addition of coating particles disrupts the engagement of the threaded components. The protruding threads also interfere with the ability to mask the opening to prevent buildup of coating material.
Many products, such as pull plugs and double washer pull plugs, are known in the art for masking surface portions of a part that is to be coated in order to prevent the coating material from contacting such surface portions during the coating process.
Pull plugs, such as those taught by U.S. application Ser. No. 10/252,197 are designed to be seated in the part opening and to conform to the shape of the opening so that the plug segment engages the wall or threads of the part opening. The flange of the plug masks the edge of the part opening preventing coating material or other contaminants from coming in contact with the part opening and any threads and from moving through the opening.
These pull plugs, however, are not desirable because they mask only the thread covered by the flange of the pull plugs allowing only one surface of the part to be coated at a time. To effectively protect the threads proximate to the undersurface of the part, the pull plug needs to be removed and reinserted in the opposite direction so that the flange now masks those threads.
Double washer pull plugs known in the art, such as the one shown in FIG. 3a, are designed to mask both sides of a threaded component (e.g., a weld nut) preventing coating particles and contaminants from damaging the threads and/or reaching the internal surface portions of the part. The design of the prior art, however, made it difficult to perfectly center the double washer pull plug inside the threaded component leaving one side partially exposed to the coating material. In addition, the difficulty in ensuring that the double washer pull plug is centered results in a variance in the range of masking quality within a single part.
It is desirable to have a plug which effectively masks both sides of a threaded or non-threaded component preventing coating error.